Torque fluctuation absorbing devices, which can absorb torque fluctuation generated between a driving power source (e.g., an internal combustion engine or an electric motor) and transmission, are widely known. Conventional torque fluctuation absorbing devices are provided with a damping mechanism, which can absorb fluctuation of driving torque transmitted to a flywheel from the driving power source, and a limiter portion, which limits torque to be transmitted from the flywheel to a transmission input shaft when fluctuating torque between the damping mechanism and the flywheel reaches a predetermined value, i.e., a limit torque value. The flywheel is connected to the driving power source, such as a crankshaft of the internal combustion engine. The damping mechanism is connected to the transmission input shaft. The damping mechanism includes frictional members that are respectively fixed to both sides of a disc at an outer circumferential portion. At the limiter portion, the frictional members of the damping mechanism are frictionally engaged with the flywheel in a direct manner or in an indirect manner via a frictional plate.
The limit torque value, at which the frictional members at the limiter portion start slipping, varies with the ages in response to the number of the operations of the limiter portion. Therefore, when the limit torque value widely increases, an excessive torque may be inputted to the transmission. As a result, the transmission may be damaged. On the other hand, when the limit torque value widely decreases, the frictional members may start slipping with a torque smaller than normal transmitting torque. In this case, torque may not be transmitted to the transmission.
Frictional powder of the frictional members, which composes of a torque limiter, seems to be one of the factors causing the above problem. In light of the foregoing, JP2003-194095A2 discloses a torque fluctuation absorbing device which forms slits communicating with the frictional member from an inner circumference portion to an outer circumference portion so as to discharge generated frictional powder into an external ambient environment by centrifugal force. The limit torque value can be stable by disposition of slits.
However, in the conventional torque fluctuation absorbing devices, frictional members, which are disposed at an outer circumference of the damping mechanism, are sandwiched by two plates. One plate is biased by a coned disk spring and the other plate is fixed to members, which rotate with the flywheel via rivets or other fixing means. This will raise the following problems.
Even when a coned disk spring 133 abuts on the opposite surface in a region wherein a second plate 132 provided at the coned disk spring 133 side and a frictional member 126 abut, if the abutting portion between the second plate 132 and the coned disk spring is deviated to the inner peripheral side (see FIG. 8A), or to the outer peripheral side (see FIG. 8B), a surface pressure distribution of the frictional surface pressure is not uniform and frictional torque is not stable. In the worst case, the second plate 132 floats up from the frictional member 126 at a portion of low surface pressure.
Within a region wherein a first plate 131, which rotates with the flywheel and the frictional member 126 abut, the bending amount at riveting area by rivets 134 is different from the area away from the riveting area in the first plate 131. This will cause the first plate 131 to be in wave shape in circumferential direction. As a result it, there is a problem wherein a high portion and a low portion are formed on an outer surface of the first plate 131. Thus the surface pressure distribution of the frictional surface pressure becomes inconstant. Therefore stability of frictional torque falls.
A need exists for providing an improved torque fluctuation absorbing device wherein a surface of a plate is flat and smooth relative to a surface of the frictional member and the surface pressure distribution is constant and frictional torque is stable.